If you want to extend the argument, then it's fair to point out that NEX has nothing at all to compete with the excellent and fairly priced 45/1.8 and 75/1.8

No, 75/1.8 is NOT fairly priced, you can get plenty 85/1.8 covering twice the image circle at less than half the price. It is in fact one of the most overpriced m43 lenses, along with 12/2 and Pana 12-35 and 35-100 pair, at least at their prices on the US market.

OK, you got me there ... in fact, it's possible that in evaluating the 45 & 75, I've drunk the kool-aid a little ... that is, I'm looking at $400 being reasonable as a "portrait prime" forgetting that 50/1.8s for larger sensors on other platforms cost much less.

In fact, I have the very excellent new Nikon 85/1.8 and it represents a tremendous bargain. (I love the FOV on APS-C).

In the 75's favor, it might be sharper across the frame ?

Well, apples to oranges, but according to DxOMark, on 24-mpix D600 Nikon 85/1.8G reaches 19P-MPix (whatever it means),

Nikon 85/1.8G @ f/1.8 on D600

while 75/1.8 on E-M5 (the best m43 camera tested) is 13 P-Mpix.

75/1.8 @1.8 on E-P5

The ancient 85/1.8D is 17P-Mpix on D600 (although obviously not wide open, the strange P-Mpix does not take that into account). On 16-mpix D7000 they are about the same as Oly75,

85/1.8G @1.8 on D7000.

on the newer 24-mpix D5200/D7100 should be better.

(I haven't bothered trying to compare since there's really no point). I'd guess it to be better built and more satisfying in use. (The Nikon feels like a consumer grade lens, like the 35 & 50). Not that I'd necessarily want to pay more for warm fuzzies like that.

I would pay more for that. The price of the tin can it is, a few $$ maybe, not $400-$500 extra.

However, if you're specifically comparing m43 to NEX, then there is no fast tele for NEX, not even a fast portrait prime. There's only the 50/1.8 which is good (maybe not 45/1.8 good) and stabilized for $350. I suspect a longer portrait prime won't be as good a bargain as the Nikon 85/1.8.